To start, I ordered a size small (5'5, 155-ish lbs). This shirt is a thicker material, but not something that becomes overbearing. I didn't feel as though I'd get overly hot or uncomfortable when wearing this in 80+ degree weather. There's plenty of room in the chest/arm region, but I will say that if you don't like things tighter on your hips/glutes, you may want to size up. I personally did not have any issues, but it's definitely something that doesn't just stretch and lay loosely around the hip region. I still found it perfectly comfortable, but this is my own preference.